1. Field of the Invention
The present invention relates to a general industrial heat (thermal) treatment apparatus that carries out a heat treatment on an object to be heated and, for example, to a heat treatment apparatus that carries out a drying process and a calcining process in a manufacturing process of a plasma display panel (PDP).
2. Description of the Related Art
A conventional PDP is manufactured by the steps of; making a front substrate by forming display electrodes on a glass substrate and laminating a dielectric layer and a protective layer over these display electrodes; making a back substrate by forming address electrodes on another glass substrate and forming a dielectric layer, partition walls and a phosphor layer on these address electrodes; and bonding these front substrate and back substrate to each other in a manner so as to allow the display electrodes and the address electrodes to intersect with each other. Here, in each of the processes in which the display electrodes and the address electrodes, the dielectric layer, the partition walls as well as the phosphor layer are formed, after a paste layer has been formed on a substrate, this paste layer is heated so as to be dried and calcined (for example, see Japanese Patent Application Laid-Open No. HEI 11(1999)-25854).
FIG. 7 is a schematic drawing that shows a conventional heating furnace 101 of a continuous type, and corresponds to a chart indicating a distribution of the furnace temperature in which positions in this heating furnace are plotted on the axis of abscissas, with substrate temperatures plotted on the axis of ordinates.
As shown in FIG. 7, the conventional heating furnace 101 is constituted by a temperature-raising unit 102, a temperature-retaining unit 103 and a temperature-lowering unit 104, and the respective units includes furnace chambers 105. In the heating furnace 101, a substrate (glass substrate) 111, used as an object to be heated, is moved in a direction of arrow 112, and allowed to pass through the temperature-raising unit 102, the temperature-retaining unit 103 and the temperature-lowering unit 104. The temperature-raising unit 102 is a unit for raising the temperature of the substrate 111 from room temperature to a temperature T, the temperature-retaining unit 103 is a unit for retaining the substrate 111 at the temperature T, and the temperature-lowering unit 104 is a unit for cooling the substrate 111 from the temperature T to the room temperature.
FIG. 8 is a schematic drawing that indicates the structure of the furnace chamber 105 of FIG. 7 and the state in which a heat treatment is actually carried out. In general, the area of a cross-section orthogonal to a transporting direction 112 of the substrate 111 is kept constant, without being changed in the transporting direction.
The furnace is used as a gas flow path in order to introduce a combustion gas thereto, discharge gases generated through the combustion, or control an atmosphere in the furnace.
However, the conventional heat treatment apparatus has the following problems.
For example, in an attempt to allow a gas to quickly flow from a certain position in the furnace to a certain further position therein, since an energy loss occurs due to a fluid resistance in the flow passage on the way, it is necessary to raise the initial velocity sufficiently. For this reason, the amount of gas supply needs to be increased, and the performance of the gas introducing mechanism needs to be improved.
In contrast, in an attempt to positively discharge burnt gases flowing through the furnace at a certain position in the furnace, the amount of discharge needs to be increased, and the discharging mechanism needs to be enlarged so as to increase the discharging efficiency. Moreover, when an object to be heated is located on the downstream side of the furnace, the quality of the object might be impaired due to a leak of discharged burning gas onto the downstream side.